Internal swelling reactions in new and existing concrete structures

Abstract

Alkali–silica reaction (ASR) and delayed ettringite formation (DEF) in concrete are major durability problems, resulting in significant maintenance and reconstruction costs for concrete infrastructures worldwide. The structures affected by this pathology are important economically and strategically since they are usually encountered in large dams, bridges, and viaducts. This type of degradation is associated with the formation of expansive products within the concrete, causing premature deterioration due to expansion and cracking. This process accelerates the ingress of moisture and other aggressive agents into the concrete, leading to further degradation of the structure. Thus, these swelling reactions can decrease the structure’s service life and, ultimately, lead to its decommissioning or demolition. During the 1920s and 1930s, several concrete structures in California, USA, were observed to develop severe cracking within a few years of their construction. In 1940, Stanton was able to demonstrate that this cracking was related to the existence of an alkali-aggregate reaction. In Portugal, the first cases were detected in the 1980s (Pracana dam and Alto Ceira dam) and 1990s (Duarte Pacheco viaduct). DEF is relatively "new" with respect to ASR, since it was only detected in the middle of the 1980s in pre-stressed concrete railway ties on the eastern coast of the United States. The occurrence of DEF in Portugal is much more recent, with the first case detected only in 2003 in prefabricated concrete railway ties. Despite decades of study, the complex reaction mechanisms of ASR and DEF have resulted in the inability to assess the risk efficiently, predict the service life, and mitigate deterioration in susceptible structures. Because of that, the problem was not eradicated, and today, numerous concrete structures still exhibit ASR and DEF. This paper offers a concise overview of managing these phenomena in both new and existing structures, emphasising reaction mechanisms, factors influencing their development, their impact on concrete, prevention in new structures, and mitigation in existing ones.